Twin hydrogen bonds with phosphine oxide: anticooperativity effects caused by competing proton donors.

In this computational work we study complexes with two equivalent intermolecular hydrogen bonds formed between trimethyl phosphine oxide and two identical proton donors ("twin" hydrogen bonds) for a set of 70 proton donor molecules. The changes in the phosphorus chemical shift and stretching frequency of the PO group upon complexation correlate quite well with the total strength of two hydrogen bonds. A set of explicit numerical dependences is proposed for assessing interatomic distances and hydrogen bond strengths from spectral data.

Deep eutectic solvent as stationary phase for flow analysis: Automated trace metal determination in food products.

Background: Deep eutectic solvents (DES) have emerged as effective solvents that address many challenges in analytical chemistry, particularly in microextraction. However, until now, their use has been primarily focused on extraction processes. This has significantly limited their application in analytical chemistry, especially in flow analysis, where the high viscosity of DES has made their use difficult.

Elucidating the isotope effect in the Morse approximation of the ground state electronic term of hydrogen molecules H, n = 1 ÷ 7. Showcasing the Herzberg anomaly and anharmonicity.

The Morse function is the simplest anharmonic approximation of the potential of a diatomic molecule, for which the vibrational Schrödinger equation could be solved almost precisely. Despite its crudeness, the Morse function has been widely used in solving various problems in molecular spectroscopy. In recent years, special attention was paid to the existence of two Morse approximations for the electronic terms U(r) of diatomic molecules, M1(r) and M2(r), which differ by the selection of primary fitting parameters and satisfactorily reproduce different parts of U(r).

1-(o-Tolyl)thiourea-based deep eutectic solvent as a stationary phase in flow injection analysis system for mercury and copper determination in edible oils.

In this work, a novel deep eutectic solvent (DES) composed of thymol and 1-(o Tolyl)thiourea 9/1 (mol) is presented for the first time. This DES has not been described in the literature. This DES was first used as a stationary phase in an extraction column integrated into a flow injection analysis system for the simultaneous determination of mercury and copper in edible oils.

Phosphine selenides: versatile NMR probes for analyzing hydrogen OH⋯Se and halogen I⋯Se bonds.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for studying the structure and dynamics of various non-covalent interactions. However, often spectral parameters that are applicable for estimation of parameters of one type of non-covalent interaction will be inapplicable for another. Therefore, researchers are compelled to use spectral parameters that are specifically tailored to the type of non-covalent interaction being studied.

Charge Relay Without Proton Transfer: Coupling of Two Short Hydrogen Bonds via Imidazole in Models of Catalytic Triad of Serine Protease Active Site.

A homologous series of 20 substituted alcohol-imidazole-acetate model complexes imitating the charge relay system in Ser-His-Asp catalytic triad of serine proteases is considered quantum-chemically. We show qualitatively that the geometries of alcohol-imidazole and imidazole-acetate short hydrogen bonds are strongly coupled via the central imidazole and such complexes are capable of effectively relaying the charge from acetate to alcohol moiety upon relatively small concerted proton displacements. We hypothesize an alternative catalytic mechanism of serine proteases that does not require two complete proton transfers or hydrogen bond breakage between Ser and His residues.

Complexes of phosphine oxides with substituted phenols: hydrogen bond characterization based on shifts of PO stretching bands.

In this work IR spectral characteristics of PO groups are used to evaluate the strength of OHO hydrogen bonds. Three phosphine oxides: triphenylphosphine oxide, tributylphosphine oxide and hexamethylphosphoramide are investigated as proton acceptors. The results of the experimental IR study and DFT calculation of 30 complexes formed by phosphine oxides with various substituted phenols or CFCHOH in CCl solution at room temperature are reported.

Internal Vibrations of Pyridinium Cation in One-Dimensional Halide Perovskites and the Corresponding Halide Salts.

We investigate vibrations of the pyridinium cation PyH = CHNH in one-dimensional lead halide perovskites PyPbX and pyridinium halide salts PyHX (X = I, Br), combining infrared absorption and Raman scattering methods at room temperature. Internal vibrations of the cation were assigned based on density functional theory modeling. Some of the vibrational bands are sensitive to perovskite or the salt environment in the solid state, while halide substitution has only a minor effect on them.

Evidence of extremely short hydrogen bond in the homoconjugated ferrocene-1,1'-diyl-bisphosphinic acid anion: sign change of the H/D isotope effect on the P NMR chemical shift.

The structure of the two intramolecular hydrogen-bonded motifs within ferrocene-1,1'-diyl-bisphosphinic acid, a cyclic dimer and a homoconjugated anion, has been experimentally revealed by NMR spectroscopy for a solution in a low-freezing polar aprotic CDF/CDFCl medium at 100 K. Structure elucidation was achieved with the help of the H/D isotope effects on the H, H and, for the first time, P NMR chemical shifts. The questions of bridging hydron localization and origins of opposite signs of H/D isotope effects on the P NMR chemical shifts in the cyclic dimer and homoconjugated anion have also been addressed by DFT calculations, including numerical solution of the Schrödinger equation for proton and deuteron vibrations in the anharmonic double well potentials.

Evolution of vibrational bands upon gradual protonation/deprotonation of arsinic acid HAs(O)OH in media of different polarity.

This computational work is devoted to the investigation (MP2/def2-TZVP) of the geometry and IR parameters of arsinic acid HAsOOH and its hydrogen-bonded complexes under vacuum and in media with different polarity. The medium effects were accounted for in two ways: (1) implicitly, using the IEFPCM model, varying the dielectric permittivity () and (2) explicitly, by considering hydrogen-bonded complexes of HAs(O)OH with various hydrogen bond donors (41 complexes) or acceptors (38 complexes), imitating a gradual transition to the As(OH) or AsO moiety, respectively. It was shown that the transition from vacuum to a medium with > 1 causes the As(O)OH fragment to lose its flatness.

The Distance between Minima of Electron Density and Electrostatic Potential as a Measure of Halogen Bond Strength.

In this study, we present results of a detailed topological analysis of electron density (ED) of 145 halogen-bonded complexes formed by various fluorine-, chlorine-, bromine-, and iodine-containing compounds with trimethylphosphine oxide, MePO. To characterize the halogen bond (XB) strength, we used the complexation enthalpy, the interatomic distance between oxygen and halogen, as well as the typical set of electron density properties at the bond critical points calculated at B3LYP/jorge-ATZP level of theory. We show for the first time that it is possible to predict the XB strength based on the distance between the minima of ED and molecular electrostatic potential (ESP) along the XB path.

Simultaneous Estimation of Two Coupled Hydrogen Bond Geometries from Pairs of Entangled NMR Parameters: The Test Case of 4-Hydroxypyridine Anion.

The computational method for estimating the geometry of two coupled hydrogen bonds with geometries close to linear using a pair of spectral NMR parameters was proposed. The method was developed based on the quantum-chemical investigation of 61 complexes with two hydrogen bonds formed by oxygen and nitrogen atoms of the 4-hydroxypyridine anion with OH groups of substituted methanols. The main idea of the method is as follows: from the NMR chemical shifts of nuclei of atoms forming the 4-hydroxylpyridine anion, we select such pairs, whose values can be used for simultaneous determination of the geometry of two hydrogen bonds, despite the fact that every NMR parameter is sensitive to the geometry of each of the hydrogen bonds.

-Interactions in 1,8-bis(dimethylamino)naphthalene -ketimine cations facilitate [1,5]-hydride shift: selective synthesis of 1,2,3,4-tetrahydrobenzo[]quinazolines.

Selective heterocyclization leading to 1,2,3,4-tetrahydrobenzo[]quinazolines from -ketimines of 1,8-bis(dimethylamino)naphthalene () under acid catalysis has been revealed. In contrast to the rather unreactive ,-dimethylaniline -ketimine, readily undergo this transformation without an additional catalyst. This distinction in the reactivity underscores the importance of the second -NMe group in , which facilitates a [1,5]-hydride shift and the subsequent cyclization.

A phosphonic acid anion and acid dimer dianion stabilized by proton transfer in OHN hydrogen bonds - models of structural motifs in blend polymer membranes.

The structure of intermolecular hydrogen-bonded complexes formed between -butylphosphonic acid and trimethylpyridine molecules has been experimentally studied as the simplest model system of the structural motifs in blend proton-conducting polymer membranes based on phosphonic acid residues. The stoichiometry of the formed complexes and proton positions in OHO and OHN hydrogen bonds were established by the H/D isotope effects and temperature dependences of the signals in H and P NMR spectra. Two structural motifs, namely, 1 : 2 and 2 : 2 acid-base complexes, were identified at the low temperature in a polar aprotic environment.

Estimations of OH·N hydrogen bond length from positions and intensities of IR bands.

In this computational work applicability of IR spectral parameters for evaluations of OH···N hydrogen bond length is discussed. For a set of 124 complexes with OH···N hydrogen bond formed by combinations of methanol/acetic acid and pyridine (and their fluorine substituted versions) geometries, energies and IR parameters were calculated at MP2/def2-TZVP level of theory. For a number of IR parameters (the shift of proton donor group stretching vibration Δν, increase of its intensity I, the low-frequency hydrogen bond stretching vibration ν, bending in-plane δ and out-of-plane γ vibrations) equations linking them with interatomic distances are proposed, the robustness and accuracy of such equations are discussed.

C, Al and Si NMR Investigation of the Hydration Kinetics of Portland-Limestone Cement Pastes Containing CH-COO-R (R=H or Na) Additives.

The hydration kinetics of Portland-limestone cement pastes with organic additives in the form of acetic acid and sodium acetate were studied by using solid-state C, Al and Si NMR spectroscopy. The evolution of the relative content of various phases was monitored over the period of one month: amorphous and crystalline calcite (in C spectra), ettringite, aluminum in C-S-H gel, calcium aluminates and calcium hydroaluminates (in Al spectra), as well as alite, belite and silicon in C-S-H gel (in Si spectra). The retarding effect of the additives on cement hydration at early age was demonstrated.

Phosphine oxides as NMR and IR spectroscopic probes for the estimation of the geometry and energy of PO⋯H-A hydrogen bonds.

In this work we evaluate the possibility of using the NMR and IR spectral properties of the PO group to estimate the geometry and strength of hydrogen bonds which it forms with OH-, NH- and CH-acids. The results of the DFT study of 70 hydrogen-bonded 1 : 1 complexes of a model trimethylphosphine oxide, MePO, with various proton donors in the gas phase and in aprotic medium (modelled as a polarizable continuum) are presented. Four types of hydrogen bonds with the general formula MePO⋯H-A were considered, where the A atom is O, C, and N (neutral or cationic acids).

Hydration of selenolate moiety: Ab initio investigation of properties of O-H⋯Se(-) hydrogen bonds in CH Se(-)⋯(H O) clusters.

This work is devoted to investigations of the influence of O-H···Se(-) hydrogen bonds on the electronic shells of selenolate R-Se(-) fragment (R═CH ). The geometric, energetic and nuclear magnetic resonance (NMR) spectral parameters for various conformers of CH Se(-)⋯(H O) clusters with n = 0-6 were calculated at CCSD/aug-cc-pVDZ level of theory. For selenolate anion CH Se(-) solvation free energy was calculated, and for water media it is equal to -71.

Noncovalent Axial I⋅⋅⋅Pt⋅⋅⋅I Interactions in Platinum(II) Complexes Strengthen in the Excited State.

Coordination compounds of platinum(II) participate in various noncovalent axial interactions involving metal center. Weakly bound axial ligands can be electrophilic or nucleophilic; however, interactions with nucleophiles are compromised by electron density clashing. Consequently, simultaneous axial interaction of platinum(II) with two nucleophilic ligands is almost unprecedented.

On the influence of water molecules on the outer electronic shells of R-SeH, R-Se(-) and R-SeOH fragments in the selenocysteine amino acid residue.

In this computational work (MP2/aug-cc-pVTZ) we investigated the features of the outer electronic shells of R-SeH, R-Se(-) and R-SeOH fragments (R = CH3), which can be considered as simplified models for the forms of the active centres of glutathione peroxidases GPx along their catalytic pathway (reduction of peroxides). It is shown that the preferential direction of a nucleophilic attack on the R-Se(-) fragment by a peroxide molecule is determined by the presence of the electron-depleted region of the selenium atom in front of the C-Se bond and nucleophilic attack can be facilitated by the solvation of R-Se(-) by water molecules. Such solvation does not block the direction of potential nucleophilic attack and also leads to the increase of the maximal value of the molecular electrostatic potential on the selenium atom.

Polymorphism and Conformational Equilibrium of Nitro-Acetophenone in Solid State and under Matrix Conditions.

Conformational and polymorphic states in the nitro-derivative of -hydroxy acetophenone have been studied by experimental and theoretical methods. The potential energy curves for the rotation of the nitro group and isomerization of the hydroxyl group have been calculated by density functional theory (DFT) to estimate the barriers of the conformational changes. Two polymorphic forms of the studied compound were obtained by the slow and fast evaporation of polar and non-polar solutions, respectively.